Method and apparatus for removing paraffin and solid deposits from an oil well



April 15, 1969 WILKERSON 3,438,444

METHOD AND APPARATUS FOR REMOVING PARAFFIN AND SOLID Filed Aug. 1. 1966 DEPOSITS FROM AN OIL WELL Sheet of 2 fi -4h TELLEE INVENTOH. /l/AA/ 5-0 W/LKEESO/U f ATTOAA/GY? i f .L E-L Apnl 15, 1969 l. E. WILKERSON 3,438,444

METHOD AND APPARATUS FOR REMOVING PARAFFIN AND SOLID DEPOSITS FROM AN OIL WELL Filed Aug. 1. 1966 Sheet 2 of 2 ISOLATION 78 I I I I I I 52-,'-""\',"L\; TOHELT/A/G I I: (FLEMEA/T v z 58 T j [ET-5 1 .L |::1".Z

v INVENTOR.

ham 6. l v/Lreesou United States Patent US. Cl. 166-304 9 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus for removing paraffin deposits from oil wells in which an elongated hollow member having an elongated heating coil therein is initially heated outside the well bore in an external heater and is then lowered into the well bore while continuing to heat the heating coil electrically. The heating coil convolutions are spaced axially from each other in the hollow member and project radially inwardly therefrom. When the hollow interior of the hollow member is at least partially filled with molten wax, lowering of the member is stopped, and the power to the heating coil is interrupted. After the wax congeals between the coils, the hollow member is removed from the well bore and the wax is removed from the interior thereof.

This invention relates to a method, and to a down hole tool, for removing paraffin and similar solid or semisolid deposits from an oil well. More specifically, but not by way of limitation, the present invention relates to a tool which can be lowered in an oil well, and which is adapted to engage paraffin deposits in the well and physically remove such deposits from the well as the tool is removed therefrom.

A number of devices have been heretofore proposed for melting or scraping parafiin deposits from oil wells in order to improve the production from such wells. Occasionally, parafiin deposits become so heavy in wells that production is stopped completely or reduced to a negligible uneconomic flow. Generally, the deposition of paraffin occurs at a relatively shallow depth in the well since, in oil wells of average depth, the bottom hole temperatures are sufliciently high to maintain the paraffin in a liquid state.

The present invention provides a method and a novel down hole paraffin removal tool which can be utilized to quickly and efficiently remove a substantial amount of the parafiin which is accumulated in an oil well, and thus permit the flow of oil through the well tubing to be increased. Broadly described, a method for removing paraffin from a well tubing in accordance with the invention comprises initially heating to a temperature exceeding the melting point of paraffin, an elongated hollow member having an outside diameter less than the inside diameter of the well tubing, and having a plurality of radially inwardly projecting protuberances on the hollow interior of the member. This initial heating is preferably carried on outside the wellhead, and the hollow casing or housing of the member, as well as the protuberances on the interior thereof, are heated at this time. The preheated hollow member is then lowered into the well tubing while continuing to heat the radially inwardly projecting protuberances in the hollow interior thereof. The lowering is continued until the hollow interior of the member is at least partially filled, and the protuberances are at least partially surrounded by paraffin. The heating of the radially inwardly projecting protuberances is then terminated to allow the protuberances and the parafiin which surrounds them to cool. After the parafiin has cooled 3,438,444 Patented Apr. 15, 1969 "ice to the solid state, the hollow member is removed from the well tubing, carrying with it a core of solid paraffin which is congealed in the interior of the hollow member, and which is retained therein by its interlocking and surrounding relationship to the radially inwardly projecting protuberances.

In carrying out the method of the invention, a novel apparatus is employed and may be broadly described as comprising a tubular, preferably cylindrical housing adapted for lowering into the well bore, the housing being open at the lower end thereof; a heating element disposed inside of the tubular housing and including portions extending radially inwardly from the internal wall of the housing and secured to the housing; and cable means attached to the upper end of the tubular housing and including an electrical lead for conducting electrical power to the heating element. This apparatus differs from the paraffin heaters of the prior art in arranging the heating element within the tubular housing so that the heating element itself includes inwardly projecting protuberances with which the congealed paraffin may be physically interlocked after it has been melted and has flowed into the tubular housing. The heating element is welded or otherwise secured firmly to the housing so that as the housing is pulled out of the well bore, the parafiin plug or core which is interlocked with the heating element inside the housing is removed with the housing.

From the foregoing description of the invention, it will be apparent that it is a major object of the invention to provide a novel and improved method for removing paraffin from a well tubing in an efiicient and expeditious manner.

A further object of the invention is to provide an economically and ruggedly constructed down hole paraflin removal tool which can be quickly assembled and run into the well tubing, and which is subject to a minimum of malfunctioning during its operating life.

An additional object of the invention is to provide a parafiin removing down hole tool which can be operated without difiiculty by personnel with a minimum of train mg.

In addition to the foregoing described objects and advantages, additional objects and advantages will become apparent as the following detailed description of the invention is read in conjunction with the accompanying drawings which illustrated a preferred embodiment of the invention.

In the drawings:

FIGURE 1 is a partly elevational, partly sectional view of the apparatus employed in the preliminary steps of the method of the present invention. The view of the portion of the well which is illustrated in section is enlarged to better illustrate structural details.

FIGURE 2 is a view in elevation of an external preheater unit used in the invention as this unit appears when viewed from one end thereof.

FIGURE 3 is a sectional view taken along line 3-3 of FIGURE 1, but showing the external preheater unit Evith the down hole paraflin removing tool removed thererom.

FIGURE 4 is a view in elevation of the down hole parafiin removal tool.

FIGURE 5 is a vertical sectional view of the down hole paraffin removing tool.

FIGURE 6 is a vertical section view of the down hole tool in the well bore showing the position of the tool at the time the last steps of the method of the invention are carried out.

FIGURE 7 is a schematic wiring diagram illustrating the manner in which the electrical power is delivered to the heating unit in the down hole paraffin removing tool as well as to the external preheater unit.

Referring now to the drawings and particularly to FIG- URE 1, an external preheating unit used in the present invention is designated generally by reference numeral 10 and, as illustrated in FIGURE 1, is being used to preheat a down hole parafiin removing tool 12 constructed in accordance with the invention. The down hole paraffin removing tool 12 is suspended on a stranded wire cable 14 which is reeved around a sheave 16 and block 18 and extends to a winch 20 mounted on a wire line truck 22. The cable 14 contains electrical leads as hereinafter described which are connected to a source of electrical power, such as a generator or similar device (not shown).

The derrick which supports the sheave 16 is positioned over an oil well designated generally by reference numeral 26 which, in accordance with conventional construction, includes a casing 28 and production tubing 30 positioned concentrically within the casing. As illustrated in FIGURE 1, the production tubing 30 has become choked or clogged with an accumulation of parafiin 32, causing production from the well to be severely decreased or terminated.

The preheater 10 comprises a segmented barrel 33 which is made up of two semicylindrical sections 34 and 36. The lower section 36 is connected to the upper section 34 by a suitable hinge 38 so that the upper section can be pivoted upwardly to permit the down hole paraffin removal tool 12 to be positioned within the barrel 33. As will be seen in referring to FIGURE 4, the paraffin removal tool 12 includes an elongated, tubular housing 40 which has an outside diameter slightly smaller than the inside diameter of the barrel 33 of the external pre heater unit 10. Each of the sections 34 and 36 of the preheater barrel 33 include a plurality of elongated heater bars 42 which extend lengthwise along the barrel, and are adapted to be heated by electrical current. The lower section 36 of the barrel 32 is secured to a plurality of upright stanchions 44 and diagonal brace members 46 which are connected at their lower ends to base plate 50 and provide a supporting framework for maintaining the preheater 10 spaced from the ground and at an angle of about 45 to the vertical as illustrated in FIGURE 1.

The details of construction of the down hole parafiin removal tool 12 are best illustrated in FIGURES 4 and of the drawings. The tool includes the elongated tubular housing 40 which, in a preferred embodiment of the invention, is cylindrical in configuration and tapers to a closed upper end 52. The lower end 53 of the cylindrical housing 40 is open, and an annular groove 54 is provided in the internal wall of the cylindrical housing and receives a metal retaining ring 56 which is snapped into the groove. A resistance type heating element 58 is Wound to a helical configuration and is disposed inside the cylindrical housing 40 to extend upwardly from the lower end thereof. The heating element 58 is a relatively large diameter electrically conducting metal member which is coiled to a diameter such that it bears against the inside wall of the housing 40. The lower end of the heating element 58, which is designated in the drawing by reference character 60, is welded to the retaining ring 56 to maintain the position of the heating coil fixed within the housing 40. A suitable electrically conducting lead 62 is connceted to the upper end of the heating element, and extends through the upper end 52 of the housing 40 and is en closed within the cable 14. The electrical lead 62 is connected to a source of electrical power as hereinafter described.

Adjacent the upper end of the housing 40 is a relief port 64 which permits air to be vented from the inside of the housing in a manner hereinafter described. A plurality of wear plates 66 are welded or otherwise suitably secured to the outside of the housing 40 at spaced intervals therealong and are constructed of a hard metal, such as tungsten carbide. The wear plates 66 function to protect the exterior of the housing 40 from contact with the Walls of the production tubing 30, and permit the down hole paraffin removal tool 12 to be more easily lowered in the production tubing without becoming hung upon joints or obstructions in the tubing.

The electrical circuitry which is employed in the practice of the present invention is illustrated in FIGURE 7. As here shown, the power source for operating the external preheater unit 10 and the heating element 58 of the down hole paraflin removal tool 12 can be a conventional 220 volt AC source as may be developed by a field generator. Connected across the power source are leads 74 and 76 which supply electrical energy to the heater bars 42 secured to the interior walls of the upper and lower sections 34 and 36, respectively, of the barrel 33 of the preheater 10. Power for the operation of the down hole tool is supplied through a solenoid switch 77, an isolation transformer 78, a variable transformer 80 and a full wave rectifier 82. The heating element 58 of the down hole tool 12 is thus supplied with a variable voltage direct current.

Operationl In the operation of the down'hole parafiin removal tool 12 of the invention, the tool is first lowered on the cable 14 to a position where it can be placed in the barrel 33 of the external preheater unit 10. The barrel 33 is made ready to receive the down hole tool 12 by opening the sections 34 and 36 of the barrel apart from each other on the hinge 38 so that the down hole tool 12 can be laid in the semicylindrical lower section 36 of the barrel, as illustrated in FIGURE 1. The upper section 34 is then closed about the tool 12 and the heater bars 42 are energized so as to heat the exterior of the housing 40 of the down hole tool. Simultaneously, the heating element 58 which is disposed in the lower end of the housing 40 of the tool 12 is energized and is brought to a high temperature. By this means, the entire length of the housing 40 is highly heated, and the heating element 58 is also brought to a high temperature preparatory to lowering the paraffin removal tool 12 in the well bore.

After the tool 12 has been heated in the external preheater unit 10 in the manner described, it is lowered on the cable 14 into the well 26 so that the housing 40 passes down inside the production tubing 30. The heating element 58 disposed in the housing 40 is continuously heated by supplying electrical current thereto as the tool is lowered in the production tubing 30. When the lower end of the housing 40 contacts the top of the paraifin accumulation 32 in the production tubing 30, the operator at the top of the well will notice a substantial decrease in the weight of the tool 12 as a result of its coming to rest on the top of the parafiin. At this time, or shortly thereafter, the power to the heating element 58 disposed in the housing 40 of the tool 12 may be shut ofl? and cooling of the heating element permitted to commence.

When the tool 40 contacts the upper end of the paraffin accumulation 32 in the production tubing 30, the highly heated, relatively thin housing 40 will cut and burn through the paralfin accumulation, melting the parafiin as it sinks downwardly in the production tubing. The molten parafiin will move upwardly in the hollow housing 40 and will surround and fill the interstices between the convolutions of the heating element 58 as shown in FIGURE 6. As the heating element 58 continues to cool, and as the housing 40 gives up its heat to the surrounding paraffin, a point in the production tubing 30 will eventually be reached where the down hole parafiin removal tool 12 can gravitate no lower in the production tubing and its downward movement will be arrested. After allowing a further, empirically determined amount of time to elapse so that the parafiin within the housing 40 can completely congeal, the down hole parafiin removal tool 12 is extracted from the production tubing 30. This is, of course, accomplished by hauling up on the cable 14. As the tool 12 is pulled upwardly in the production tubing 30, it carries with it the congealed core of paraflin located within the housing 40. This parafiin core has become rigidly interlocked with the heating element 58 and thus cannot slide out of the housing 40.

When the tool 12 with the parafiin core enclosed within the housing 40 has been extricated from the well 26, the tool is again placed in the external preheater unit and the heater bars 42 and the internal heating element 58 are both energized to heat the housing and the heating element 58 to a high degree. This causes the paraffin core within the housing 40 to melt and to gravitate from the lower end 53 of the housing and out of the lower end of the barrel 33 ofthe external preheater unit 10. Heating of the tool 12 is continued until it is thoroughly cleaned of paraffin and is brought to a temperature sufiiciently high to permit it to be once again lowered in the production tubing 30. The process of cyclically lowering and extricating the down hole paraflin removal tool 12 is then repeated a sufficient number of times to completely remove the paraffin obstruction in the production tubing.

From the foregoing description of the invention, it will be apparent that the invention provides a simple apparatus, and a relatively easily practiced method for completely and quickly removing an accumulation of paraffin from an oil well. No special training is required in order to properly utilize the apparatus, and to practice the method of the invention, and the equipment provided for practicing the method is ruggedly constructed and characterized in having a long and trouble-free operating life.

Although a preferred embodiment of the invention has been herein illustrated in order to provide an example of one way in which it is anticipated the invention can be successfully practiced, it is to be understood that certain equivalent procedures and structures can be used without departure from the spirit and scope of the invention. All such equivalent structures which continue to rely upon the basic principles of the invention are therefore deemed to be circumscribed by the spirit and scope of the invention except as the same may be necessarily limited by the appended claims or reasonable equivalents thereof.

What is claimed is:

1. A method for removing parafiin from a well comprising:

heating to a temperature exceeding the melting point of the paraffin, an elongated hollow member having an outside diameter less than the inside diameter of the well bore and having a plurality of radially inwardly projecting protuberances on the hollow interior of the member;

lowering the heated hollow member in the well bore while heating the radially inwardly projecting protuberances, said lowering being continued until the hollow interior is at least partially filled, and the protuberances at least partially surrounded, by parafiin; then terminating the heating of said protuberances to allow the protuberances and parafiin to cool; and

after the paraffin in the hollow interior of the member has cooled to a solid state, removing the hollow member from the well bore with a core of paraffin in the interior thereof.

2. The method claimed in claim 1 wherein said radially inwardly projecting protuberances are formed and positioned in the interior of said hollow member by helically coiling an electrically conducting resistance element in the interior of the hollow member along the inside wall thereof.

3. The method claimed in claim 1 wherein said hollow member is heated before lowering it in the well bore by placing the hollow member in a surrounding heated environment exterior of the well bore and simultaneously heating said protuberances by the application of electrical energy thereto.

4. The method claimed in claim 3 and further characterized to include the step of removing parafiin from the interior of said elongated hollow member after it is removed from the well bore by placing the elongated hollow member in said heated environment.

5. The method claimed in claim 3 wherein said surrounding heated environment and said protuberances are both heated by electrical energy derived from a common source.

6. A method for removing paraffin from a well comprising:

lowering into the well, an elongated, tubular member having an open lower end and having paraflin retaining elements thereon;

heating the tubular member sufficiently to permit it to move downwardly into the parafiin accumulation in the well until the paraffin retaining elements are contacted by the paraffin;

cooling the tubular member sufficiently to permit molten paraffin to congeal where it contacts said paraffin retaining elements; then removing the tubular member from the well; and

heating the tubular member to melt paraflin carried thereby to remove the paraffin from the tubular member.

7. Apparatus for removing paraiiin from a well bore comprising:

a tubular housing adapted for lowering into the well bore, said housing being open at the lower end thereof;

a heating element disposed stationarily inside said tubular housing and including portions extending radially inwardly from the internal wall of said housing;

cable means attached to the upper end of said tubular housing and including an electrical lead for conducting electrical power to said heating element;

means secured to said cable means at a distance from the upper end of said housing for pulling said cable means and housing upwardly in the well bore and lowering the cable means and housing in the well bore;

guide means intermediate the length of said cable means for aligning said cable means and housing with the well bore, and alternatively, permitting the cable means and housing to be swung out of alignment with said well bore; and

a preheating device to one side of said guide means and having a tubular barrel dimensioned to receive and enclose said tubular housing for heating said housing before it is lowered in said well bore.

8. Apparatus as claimed in claim 7 and further characterized to include:

a source of electrical power; and

electrical circuitry interconnecting said source of electrical power with said pre-heating device and the heating element disposed stationarily inside said tubular housing.

9. Apparatus for removing paraffin from a well bore comprlsmg a tubular housing adapted for lowering into the well bore, said housing being open at the lower end thereof;

means for lowering the tubular housing in the well bore and adapted to be located above the well bore;

a preheating device located to one side of said lowering means and having a tubular barrel dimensioned to receive said tubular housing for heating said housing before it is lowered in said well bore;

a helically configured heating element disposed stationarily inside said tubular housing and bearing against the internal wall of the tubular housing and extending upwardly in the housing from the lower end thereof, said helically configured heating element including axially spaced convolutions extending radially inwardly from the internal wall of said housing; and

cable means attached to the upper end of said tubular housing and including an electrical lead for conducting electrical power to said heating element, said cable means extending from the upper end of said tubular housing to said lowering means.

References Cited UNITED STATES PATENTS 8 Booth 166-60 Bowman 219278 X Welge et a1 166-60 X Cotter et a1 166-60 5 DAVID H. BROWN, Primary Examiner.

US. Cl. X.R. 

